Not Applicable
Not Applicable
This invention relates to an apparatus for removing semiconductor wafers from within the runner disks of a double-sided polishing machine.
It is known to work semiconductor slices or wafers (SC wafers) by means of polishing machines in such a way that a high degree of smoothness, non-defectiveness, and fineness of the surface is obtained. Such a double-sided polishing machine has become known from DE 195 47 086. Runner disks having three apertures, for example, to receive SC wafers interact with an outer and an inner pinned rim and are rotationally advanced if at least one of the pinned rims is driven. This causes the SC wafers to perform a cycloidal motion which is overlain by the rotation of the working disks. Thus, it is possible to machine parallel-sided surfaces on work pieces at a high accuracy.
The known machine also makes it possible to position the runner disks for the loading or unloading of the SC wafers. While this does not apply to the circumference of the runner disks it does apply to the center thereof. Hence, it is possible to stop the center of a runner disk at a predetermined point, using the drive of at least one pinned rim.
The runner disks have been fed and unloaded again by hand hitherto. Any manual handling of a freshly polished SC-wafer involves the risk that its polished surface might be damaged, e.g. by producing marks or scratches. Particularly critical are those damages which cover the front side of the SC wafer. Also, freshly polished SC wafers are extremely sensitive to non-controlled attack by chemicals such as an etching agent. As is known the polishing of such SC wafers using the machine described is a mechanical and chemical process. Any further chemical impact of the polishing agent is detrimental upon completion of the polishing process and, therefore, requires to be stopped as rapidly as possible, e.g. by transferring the SC wafer to a rinsing, neutralizing or cleaning bath.
Since the double-sided polishing operation on SC wafers as described is a so-called batch process a large number of SC wafers needs to be removed as rapidly as possible upon completion of the process.
It is the object of the invention to provide a device for removing SC wafers from within the runner disks in a double-sided polishing machine in which the SC wafers may be rapidly removed and deposited in an automatic manner with no manual step. Furthermore, the SC disks are intended to be removed in a desired order.
The inventive device provides a suction head which may be connected to a vacuum and, in one aspect of the invention, may have one or more suction cups. These suction ports or suction cups are designed so that all of the SC wafers of a runner disk can be gripped and raised simultaneously. The suction head is adapted to be rotated by means of a votary drive for an alignment towards the SC wafers lying in a runner disk. The suction head, after being a swiveled to a lay-down device, may be adjusted again in a predetermined aligned position towards the lay-down device.
The suction head is rotatably supported on an arm, preferably a swivel arm which, in turn, is rotatably or adjustably supported about a vertical axis. In addition, the arm is adjustable in height by means of a lifting drive. A control device is provided for the individual drives to control the position of the arm and the suction head above a runner disk and the lay-down device.
As was already mentioned at the beginning the polishing machine is capable of precisely controlling the runner disks in their position between the pinned rims. Therefore, it is possible to precisely position each runner disk with respect to the removing apparatus. Hence, it is readily possible as well to use the control device for moving the arm to a position in which the axis of rotation of the suction head is aligned towards the center of a runner disk. Rotating the suction head will then make it possible to associate the suction ports and suction cups with the SC wafers received in the runner disk. In one aspect of the invention, this can be accomplished by the fact that a mark, e.g. a bore, is associated with a reception aperture of the runner disk and the suction head has a sensor for detecting the mark.
It is desirable and even prescribed frequently to take the SC wafers out of the polishing machine in the order in which they were inserted. For example, if the first SC wafer is placed by hand or machine in that reception aperture of the runner disk to which the mentioned marking belongs and further insertion is effected in a predetermined sense of rotation it will also be possible to deposit the SC wafers on a lay-down device in a predetermined orientation so that they may be conveyed, for example, to a reception cassette in the same direction as the one while they were loaded from the lay-down device.
In another aspect of the invention, the lay-down device has a circular plate adapted to be driven by a rotary drive which is subdivided into three sectors wherein each sector has at least one nest to receive a semiconductor wafer and is supported so as to be tiltable about a horizontal axis and one sector each is adapted to be aligned towards a transfer portion leading to a cassette. When a sector is tipped with an SC wafer received therein this one will slide, for example, on a film of a conveying liquid, to a reception cassette. Such a device has been known as such. The receiving circular plate is already in a liquid bath so that scratches or other harms to the surface are avoided during the conveyance described.
Preferably, the suction head has two suction cups for each SC wafer being removed, which cups lie on a radius of the SC wafer when the suction head is aligned towards the SC wafers. Preferably, a suction head will then lie aligned towards the center of the SC wafer.
Immersion baths are provided for the suction cups in the nests of the lay-down device and the lay-down circular plate. This allows to keep the suction heads wet and to rinse them during a break.
One aspect of the invention provides that the arm is pivotally supported about a vertical axis in a bearing component and is driven by a semirotary drive and that the bearing component is movably supported along a linear guide which is arranged between the polishing machine and another polishing machine where the bearing component is adapted to be displaced by an actuator drive along the guide. In this aspect of the invention, the unloading apparatus is capable of alternatively being employed on one of two polishing machines disposed next to each other by means of a linear transfer device. The mode of operation allows for two different options. First, the inventive unloading apparatus is able to effect the removal of wafers from within two double-sided polishing machines (single-stage process). The rate of process time in the unloading time is about 5%. Therefore, the unloading apparatus is preponderantly in a stop position. If two machines are linked by the inventive unloading apparatus the cost per SC wafer removed will be correspondingly lower. Furthermore, some mounting area and, possibly, an operator will be saved. One operator is required for each plant in case of two individual plants. In the inventive unloading apparatus, one operator may attend to two plants by using one unloading apparatus.
The inventive unloading apparatus may also be employed for a two-stage process in case of two double-sided polishing machines. At this point, the SC wafers, after undergoing machining, are transferred by means of the unloading apparatus from a first machine to the second machine which effects finishing. After finishing, the removing or unloading apparatus may deposit the SC wafers in the wet stockpiler.
It is known to support the upper polishing plate in a swivel-away position with respect to the lower one in order that there be a free access to the runner disks and SC wafers. If two double-sided polishing machines are disposed next to each other when the inventive unloading apparatus is used it is useful, therefore, to design the individual machines in such a way that the upper polishing plate be always swivelled away in a direction opposed to the polishing plate of the other machine in order that the machines may be juxtaposed very close to each other.